Electric motor



Aug. 27, 1946. R. LEE

ELECTRIC MOTOR Filed Nov. 30, 1942 .m mwN A 1188@ KW v um w mw 4 @Nbw Smww mNQN NSUH. H NN Qm.

01 /NVENTOR I ROYAL LEE y ATTORNEY will Patented ug. 27, 1946 UNITEDSTATES rar; ortica ELECTRC MOTOR Applicationv November 30, 1942, SerialNo. 467,336

2 Claims.

The present invention relates to electric motors and to rotary toolsembodying the same,

An object of the invention is to provide an improved and efficientelectric mo-tor adapted for incorporation in a power tool, such as aportable drill, the motor being so constructed and arranged as to berelatively compact in a transverse dimension for permitting use of thetool in confined spaces.

Another object is to provide an electric motor having an improved statorstructure which affords short and eiiicient magnetic circuits.

A further object is to provide a portable motor driven tool havingsimple and easily manipulated means for controlling the motor speed.

The invention further consists in the several features hereinafterdescribed and claimed.

In the accompanying drawing,

Fig 1 is a side elevation of a motor-driven drilling tool constructed inaccordance with the invention;

Fig. 2 is a top View of the tool;

Fig. 3 is a front end view of the tool;

Fig. 4 is a longitudinal sectional elevation of the tool and motorthereof, taken generally along the line 4-4 of Fig. 2;

Fig. 5 is a transverse sectional elevation of the tool and motorthereof, taken generally along the line 5-5 of Fig. 4;

Fig. 6 is a detail sectional View taken generally along the line G-- ofFig. 5;

Fig. 'l is a detail View of associated field laminau tions for themotor, and

Fig. 8 is a top view of a multiple tool mounting.

Referring to the drawing, the electric motor for the tool comprises amagnetizable stator core, preferably of laminated construction andformed by complementary half-sections IS, and a cooperating rotor crarmature I I carried on a shaft I2. The stator core is in the form of anelongated loop, preferably of generally elliptical shape and truncatedat both ends. Each half-section IU of the stator core is U-shaped, asseen in Figs. 5 and '7, and has a yoke portion i3 and curved legs I4diverging from the yoke portion and tapering toward their ends. The yokeportion of each core section carries a magnetizing winding or eld coilI5 which is accommodated within a notch I6 formed at the inner side ofthe core section. The two field coils are substantially identical, andin the case of the two-pole motor illustrated these coils are soarranged that the adjacent legs of the two stator core sections have thesame polarity. The stator core legs have concave inner sides II formingpole faces adjacent to the rotor,

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these pole faces being chamfered near the field coils. The assembledstator core presents op posed consequent poles each of which is formedby adjacent legs of the two stator sections. The free end portions ofthe core legs are relatively thin and the aligned extremities of theadjacent legs are in proximity to each other at the polar axis, the legsbeing either in abutment or separated a short distance by an interveningair gap or by interposed non-magnetic material, such as in sulation I8,Fig. 5. The insulation may be varnish coatings, or strips of insulatingmaterial, or merely the oxide coating of the stator laminations. In anycase, there is a region of high reluctance between the relatively thinends of the stator core legs, so that the two parallel magnetic circuitsthrough the stator core sections are more or less independent of eachother, and it is unnecessary to effect critical adjustment of the numberof turns in the two field coils. The high reluctance between the ends ofthe stator core legs also reduces twisting or distortion of the field byarmature reaction. The shape and arrangement of the stator core resultin short and efficient magnetic circuits and make it possible to obtainthe desired magneto-motive force with relatively small and compact fieldcoils and with relatively few turns in the coils. The overall width ofthe stator core in the direction of the polar axis is only slightlylarger than the diameter of the rotor.

The electric motor is preferably of the variable speed series oruniversal type operable on both direct current and alternating current,but in some instances the motor may be of other types, such as shunt,compound, repulsion, induction, and synchronous.

The laminated stator core sections are carried by studs or rods I9extending through the legs of the sections parallel to the motor shaftand secured to end frame members 2i) and 2i of elliptical shape, eachstud having a sleeve nut 22 between the core section and the framemember 2l and a sleeve '23 (which may also be a nut) between the coresection and the frame member 26. Each stud also has a clamping nut 24bearing on the frame member 26. Each of the frame members 20 and 2l hasa width in the plane of the polar axis slightly larger than the diameterof the armature. A thin non-magnetic casing member or shell 25 of narrowelliptical shape fits snugly around the assembled stator core sections,and at its ends the casing member fits into rabbeted marginal portionsof the end frame members, the casing member being flush with these framemembers. The casing member 25 is vpreferably of metal, although in someinstances other materials, such as hardened plastics, may be used.

A gear casing is secured to the front frame member 20 by sleeve nuts 21engaging the studs I9, the gear casing being of elliptical shape, asseen in Fig. 3. A loop-shaped handle 28 has an elliptical front portionsecured to the rear frame member 2i by sleeve nuts 29 engaging the studsI9, there being a short elliptical casing member or shell 30 interposedbetween the handle and this frame member to form a governor chamber. Thehandle includes at its rear a hollow handgrip portion which extendstransversely of the projected axis of the rotor.

The rear frame member 2l carries an insulating block 3| supportingtherein a ball bearing 32 for the rear end of the motor shaft I2, andthe front frame member 29 supports therein a ball bearing 33 for thefront end of the motor shaft. The armature has a commutator 34 on whichbear opposed spring-pressed brushes 35 slidable in tubular brush holders3B, the latter being se cured to the insulating block and extendingalong the major axis of the narrow elliptical frame member 2l. Screwplugs 36' are secured in the frame member 2| for access to the brushes.The insulating block also carries spring-pressed brushes 3'! for asuitable speed governor 38 mounted on the adjacent end of the motorshaft, the brushes 3l extending parallel to the shaft axis. The governormay be or the general type shown in my Patent No. 1,767,146, dated June24, 1930. Ihe governor includes separable springn mounted contacts 39and a speed-adjusting lever the latter having a free end portion at theaxis of the motor and being actuated by an axially extending stem elforming part of a 1ingeiwoperated control member 42 slidably mounted inthe front and rear portions of the handle.

-The control member' is urged to motor-stopping position by a leafspring 43 housed in the hollow grip portion of the Ihandle and ismanually retractable, in the manner of a trigger, against the action ofthe spring to start the motor and. to effect an increase in motor speed.In some instances, the governor contacts may form a motorstoppingswitch. rIhe leaf spring t3 is carried by a top plate 44 detachablysecured to the `handle. A screw 45 is secured to the top plate andextends into a slot 46 in the control member to guide and limit thetravel of the control member.

The handle 23 has electric supply conductors 4l attached to its lowerend, these conductors being connected to the motor windings through adetachable connector plug 48.

r'he front end of the motor shaft has a pinion i9 which extends in thegear casing 26 and which meshes with a gear 50 on an intermediate shaft5|, the latter being supported by ball bearings 52 in the frame member29 and gear casing 26. The intermediate shaft has a pinion 53 whichmeshes with a gear 54 on a chuck shaft 55, the latter having a chuck 56at its front end to receive a drill or other tool element. The chuckshaft ls supported by a ball bearing 51 in the frame member 20 and by aroller or needle bearing 58 mounted in a cylindrical projection 59 ofthe gear casing, there being a ball bearing `6l) in the projection toresist axial thrust on the shaft.

In operation, the motor-driven tool is held and guided by the handle 28,and the speed of the motor is adjusted by manually pressing the governorcontrol member 42 rearwardly so as to permit the drill or other toolelement to rotate at the desired speed and to avoid damage to the toolelement by excessive speed. As the casing or housing of the tool isrelatively narrow, being only slightly wider than the rotor diameter,the

tool can readily be inserted into narrow or confined spaces.

Because of the high eiliciency of the motor, it is ordinarilyunnecessary to provide for ventilation of the motor, thus avoiding theuse of air openings in the casing portion of the motor.

For certain tool operations, a number of the rotary tools may bearranged in a group or battery, as indicated in Fig. 8, in which eventthe parallel chuck shafts of the tools can be brought relatively closetogether because of the narrow'- ness of the tool housings. The toolsmay be mounted in any suitable manner, as by clamping the gear casingprojections 59 in respective openings i formed in a support 52.

While the invention particularly relates to electric motor structuresand to rotary power tools incorporating the same, certain features ofthe invention are also applicable generally to dynamo-electric machines.

What I claim as new and desire to secure by Letters Patent is:

l. In an electrically-operated tool, a housing, a variable-speed motorin said housing having a magnetizable stator and a tool-driving rotor,said housing having a frame member adjacent to an end of said rotor, ahandle .secured to said frame member, a speed-responsive governor forthe motor disposed between said frame memberand Y handle, and a manuallyoperable speed-setting actuator for the governor shiftably mounted insaid handle, said handle having a hand-grip and a hand-receiving openingin front of said handgrp, and said actuator having a iinger-operatedtrigger portion within saidopening.

2. In a dynarnoelectric machine, the combination of a stator, a rotorcooperating therewith and having a commutator and a shaft,speed-responsive switch means having a current-conducting rotary membercarried by said shaft, an insulating block interposed between saidcommutator and rotary member, said rotor shaft being journalled in saidblock, brush means for said commutator carried by said block at one sideof said block, and brush means for said rotary member carried by saidblock at the other side of said block.

ROYAL LEE.

